In recent years, surface acoustic wave filters have been used for bandpass filters in an RF module of portable electronic devices, such as cell phones, smart phones and tablet computers.
FIG. 1 is a plan view diagram of a common surface acoustic wave filter device. The surface acoustic filter (SAW) device 10 comprises a first interdigitated transducer (IDT) configuration 11, a second interdigitated transducer (IDT) configuration 13 and a piezoelectric substrate 15. The first IDT configuration 11 and the second IDT configuration 13 are arranged on the piezoelectric substrate 15, and the first IDT configuration 11 and the second IDT configuration 13 are adjacent to each other.
The first IDT configuration 11 comprises two facing comb-shaped electrodes 111/113, and the second IDT configuration 13 comprises two facing comb-shaped electrodes 131/133. When an input voltage Vin is applied to the first comb-shaped electrode 111 and the second comb-shaped electrode 113, a surface acoustic wave is generated on the surface of the piezoelectric substrate 15 and is transmitted from the IDT configuration 11 to the second IDT configuration 13 via a gap 12. Then, the second IDT configuration 13 convers the surface acoustic wave to an output voltage Vout.
However, the surface acoustic wave that is transmitted from the first IDT configuration 11 to the second IDT configuration 13 via a gap 12 may be scattering into the piezoelectric substrate 15, causing BAW Scattering and insertion loss.